In food packaging, in particular, in packaging of perishable foodstuffs such as meat, fresh fishes, and fruit and vegetables, there have been extensively used stretch films that are excellent in transparency, flexibility and heat sealability. As the film of this type, there have been generally used those films produced from a polyvinyl chloride-based resin composition prepared by compounding an adipic acid ester-based plasticizer and various anti-fogging agents in a polyvinyl chloride-based resin.
With respect to the films for food packaging, importance is attached to hygiene of compounding agents and migration thereof into food, etc. Therefore, these films have been regulated by FDA Standard (Food and Drug Administration) in Unites States, and by PL Standard (Voluntary Restraint Standard relating to Vinyl Chloride Resin Packaging Containers and the like), and resins, additives, etc., which are capable of conforming with these Standards have been used in a film for food packaging. In addition, as the testing method for confirming migration of additives into food, etc., such an extraction testing method defined as an evaporating residue testing method according to the Ministry of Health and Welfare Notice No. 20 has been conducted.
In the aforementioned background, with respect to a film for food packaging which is produced mainly from polyvinyl chloride, or a resin composition used for preparing the film, for example, in Patent Literature 1, there is described a vinyl chloride-based resin composition for food packaging which comprises a polyvinyl chloride-based resin, and an aliphatic polybasic acid-based polyester plasticizer and a glyceryl ester as an edible plasticizer which are used in the above resin.
In Patent Literature 2, there is described a food packaging material comprising 100 parts by mass of a chlorine-containing resin such as a polyvinyl chloride-based resin and 1 to 50 parts by mass of an epoxidized soybean oil produced by a hydrogen peroxide method which has a peroxide value of not more than 13 and comprises no specific phosphorus-based antioxidant.
In Patent Literature 3, there is described a stretch film comprising 100 parts by mass of a polyvinyl chloride-based resin, 15 to 45 parts by mass of a specific adipic acid ester-based plasticizer, 1 to 30 parts by mass of an epoxidized vegetable oil, 11 to 40 parts by mass of a polyester-based plasticizer having an average molecular weight of 1000 to 3000, and 0.1 to 1.0 part by mass of a higher fatty acid having 8 to 22 carbon atoms.
In Patent Literature 4, there is described a polyvinyl chloride-based resin composition comprising 100 parts by mass of a polyvinyl chloride-based resin, 17 to 21 parts by mass of a mixture of an aliphatic polybasic acid-based polyester-based plasticizer having a weight-average molecular weight of 800 to 3,000 and an aliphatic polybasic acid-based ester-based plasticizer (in which the content of the aliphatic polybasic acid-based polyester-based plasticizer is 20 to 40% by mass), 3 to 9 parts by mass of an epoxidized vegetable oil, and 0.5 to 3.0 parts by mass of a glycerol ester compound as an antifogging agent.
As described above, the plasticizer is conventionally added to the food packaging films comprising polyvinyl chloride as a main component to enhance the flexibility thereof. Among these food packaging films, in particular, wrap films for food packaging are required to have a high flexibility. For this reason, even though the plasticizer is added in such an amount as described in Patent Literature 4, the resulting films tend to have an insufficient flexibility. On the other hand, if the amount of the plasticizer added is increased, the amount of the plasticizer eluted from the films tends to be increased. Thus, it may be difficult to satisfy both a good flexibility of the obtained films and a less elution of the plasticizer from the films at the same time.
Also, in the technology described in Patent Literature 3, since the polyester-based plasticizer having an average molecular weight of 1000 to 3000 is a relatively readily elutable plasticizer, it may be difficult to ensure a practically sufficient anti-elution property (safety) of the resulting films.
In addition, in the technology described in Patent Literature 1, the use of the aliphatic polybasic acid-based polyestyer plasticizer solely tends to fail to exhibit a sufficient plasticizing effect, and if the amount of the glycerol ester added is increased, the amount of the plasticizer eluted from the films tends to be increased, so that it may be difficult to satisfy both of a good flexibility of the films and a low elution of the plasticizer from the films. Also, although the epoxidized soybean oil or the like as described in Patent Literature 2 which is a plasticizer derived from natural substances are suitably used for food packaging, the plasticizer of this type not only tends to be readily eluted from the films, but also tends to suffer from deterioration in appearance of the obtained films upon storage.
In the case where the film to which a large amount of the epoxidized soybean oil is added, is stored at a low temperature, the surface of the film tends to be whitened owing to solidification of the soybean oil bled out thereon, which results in poor appearance of the film. On the other hand, in the case where the film to which a large amount of the epoxidized soybean oil is added, is stored under the high-temperature and high-humidity condition, the epoxidized soybean oil bled out on the surface of the film tends to be reacted with water and polymerized, so that the surface of the film tends to be whitened, which also results in poor appearance of the film. Thus, in the technology described in Patent Literature 2, it may be difficult not only to satisfy both a good flexibility of the film and a low elution of the plasticizer therefrom, but also to provide a food packaging film having an excellent appearance.
Consequently, the food packaging film has been frequently required to have not only a good low-elution property (safety) and a good packaging suitability (flexibility), but also a good appearance. However, the conventional films have failed to satisfy all of good low-elution property, packaging suitability and appearance, and therefore there is a strong demand for films that are improved in their properties.